Cephalometry Flashcards
Why is Angles not enough to determine skeletal relationships
he hypothesises that 1st perm molars represented the position of mx and md but we now know this is an oversimplification –> lacked objective way of measuring skeletal relationships
What is a Cephalostat. What is a problem?
X-ray machine set at fixed distance between source and patient + patient and sensor
Taken with standardised head position - natural head position (pt looks into own eyes, head will always be level)
Aluminium wedge blocks some rays going into soft tissues to allow better definition
No standardisation between manufacturers –> need to calculate and compare magnifications
T/F increased magnification of film increases angle
F. doesnt matter how magnified (distance changes - linear) angle doesnt change
Goals of cephalometric analysis (5)
Objectively measure relationship between 5 major functional components of the face
- Cranium and cranial base
- Maxilla
- Mandible
- Maxillary dentition
- Mandibular dentition
Cranial landmarks (forming cranial base) how can we use it?
Nasion (Na) - anterior point of intersection between nasal and frontal bones
Sella (S) - midpoint of the cavity of sell turcica
–> line between the two forms cranial base
goal - if we assume cranial base is stable, we can see how other structures are positioned relatively
Maxilla Landmarks
ANS - the tip of of anterior nasal spine
PNS - tip of posterior spine of palatine bone at the junction of soft and hard palates
Point A - innermost point of contour of the premaxilla between ANS and incisor tooth
Mandible landmarks
Point B - inntermost point on contour of md between incisors and bony chin
Pogonion (Pog) - most anterior part on contour of chin
Menton (Me) - most inferior point of md symphysis
Gonion (Go) midpoint of contour connecting ramus and body of md
Dental landmarks
U1 - upper incisor tip and apex L1 - lower incisor tip and apex U6 - upper 1st molar L6 - lower 1st molar
Name all landmarks
top back - Sella (S)
top front - Nasion (Na)
middle back - PNS
middle front - ANS
middle below - Point A
low back - Gonion (Go)
low bottom - Menton (Me)
low front - Pogonion (Pog)
low front - Point B
blue - dental landmarks U1, L1, U6, L6
How do you evaluate sagittal jaw relationship and what does it mean.
What is normal?
ANB angle
shows discrepancy of upper and lower jaws in relation to cranial base
normal = 3 (S.D. 2) 1-5 degrees
3 = class I >5 = class II <1 = class III
e.g. mild class II = 6, severe class II = 15
How to evaluate which jaw is causing the problem?
SNA and SNB angles (whichever not normal) –> used to establish relationship of md and mx to cranial base whereas ANB is used to establish mx and md to eachother
SNA = 81% S.D. 3
<78 retrognathic mx
>84 prognathic mx
SNB = 78% S.D. 3
<75 retrognathic md
>81 prognathic md
What does facial convexity mean? What are the variations and what do mean?
deviations from ideal facial convexity results from disproportion in size of jaws
straight or slightly convex = class I
convex = class II
concave = class III
ANB, SNA, SNB evaluate the A-P (sagittal plane) but you can also assess skeletal (vertical plane). How?
maxilla/mandible plane angle (MMPA)
Normal 27 (S.d. 4) Short face >23 (brachyfacial) Long face >11 (dolichofacial)
Define the facial types?
Brachyfacial - broad, square face, prominent chin, reduced mandibular angle
Mesofacial - generally balanced facial features
Dolichofacial - long, narrow face, reduced chin projection, increased mandibular plane angle
Dental relationships
Mx - PNS -ANS line in relation to U1
Md - Go-Me line in relation to L1
Calculate magnification of a cephalogram based on distances between the patient and x-ray source; and film/sensor.
A = distance between source and patient
B = distance between patient and sensor
(A + B)/A x100 = % of magnification
